1. Field of the Invention
The present invention relates to a helicopter power transmitting apparatus for transmitting torque generated by a helicopter engine to a main rotor, etc., and more specifically to a power transmitting apparatus for transmitting engine rotational torque to the main rotor through a single input gear shaft in mesh with a plurality of gear trains uniformly, where the torque is equally transmitted to each gear trains, in order to reduce the weight and size of the apparatus.
2. Description of the Prior Art
The helicopter power transmitting apparatus is an apparatus for transmitting a rotational torque generated by a helicopter engine to a main rotor, a tail rotor, an electric dynamo, a hydraulic pump, etc., whose arrangement on a helicopter is shown in FIG. 7. In FIG. 7, an output shaft 41 of an engine 40 is linked with a power transmitting apparatus 42, and a drive shaft 43 extending from the power transmitting apparatus 42 drives a main rotor 44. In addition, a tail rotor drive shaft 45 extends from the power transmitting apparatus 42 to drive a tail rotor 46.
In the helicopter power transmitting apparatus of the above-mentioned prior art, since both light-weight and small-size characteristics are severely required, it is effective to adopt such a construction that double gear trains are provided for a single input shaft linked with an engine output shaft so that the engine rotational torque can be transmitted to a large-diameter gear for driving the main rotor through a pair of gear trains, as disclosed by a document xe2x80x9cA 2400 Kw Light Weight Helicopter Transmission with Split-Torque Gear Trainsxe2x80x9d: ASME 84-DET-91. In this prior art, the helicopter power transmitting apparatus is such that the rotational torque applied to a single input shaft is transmitted to a large-diameter main rotor driving gear through the pair of the gear trains, since there inevitably exist some manufacturing tolerance, shaft deformation, etc., it has been difficult to uniformly transmit the rotational torque to the main rotor through the pair of the gear trains as expected.
With respect to this apparatus, a related art already filed in Japan by the same Applicant as Japanese Patent Application No. 6-80475 will be first explained with reference to FIG. 8, in which the helicopter power transmitting apparatus is provided with the pair of the gear trains for automatically distributing the rotational engine torque uniformly.
As shown in FIG. 8, in this helicopter power transmitting apparatus 51, a largediameter gear 53 is directly linked with a main rotor drive shaft 52. This largediameter gear 53 is in mesh with a pair of first and second small-diameter gears 54a and 54b having the same diameter and the same number of teeth and arranged at a predetermined angular interval.
A first largediameter helical gear 56a is linked with the upper side of a first shaft 55a of the first small-diameter gear 54a. Further, a second largediameter helical gear 56b is fixed to the lower side of a second shaft 55b of the second smalldiameter gear 54b. The first largediameter helical gear 56a and the second largediameter helical gear 56b are the same diameter and the number of teeth, but opposite to each other in the inclination direction of the helical gear, so that the thrust directions generated by the two largediameter helical gears 56a and 56b are determined opposite to each other.
An input shaft 57 is arranged between the two first and second shafts 55a and 55b roughly in parallel to the two shafts 55a and 55b. Further, an outer cylinder 58 is arranged so as to be axially and slidably fitted to the outer side of the input shaft 57. Further, a first smalldiameter helical gear 59 in mesh with the first largediameter helical gear 56a and a second small-diameter helical gear 59xe2x80x2 in mesh with the second largediameter helical gear 56b are arranged on the upper and lower ends of the outer cylinder 58, respectively.
The first smalldiameter helical gear 59 and the second smalldiameter helical gear 59xe2x80x2 are the same in diameter and the number of teeth, but opposite to each other in the inclination direction of the helical gear, so that the thrust directions generated by the two smalldiameter helical gears 59 and 59xe2x80x2 are determined opposite to each other.
Further, on the lower end of the input shaft 57, two bevel gears 60 and 61 are arranged to transmit the rotational torque generated by the engine to the power transmitting apparatus 51. In addition, a gear 62 is in mesh with the largediameter gear 53, to drive a tail rotor drive shaft 65 through two bevel gears 63 and 64.
In the above-mentioned conventional helicopter power transmitting apparatus 51, the rotational torque applied to the input shaft 57 is transmitted to the largediameter gear 53 via two transmission routes. That is, the first transmission route is to transmit the rotational torque of the input shaft 57 to the largediameter gear 53 by way of the outer cylinder 58, the first smalldiameter helical gear 59, the first largediameter helical gear 56a, and the first small-diameter gear 54a. Further, the second transmission route is to transmit the rotational torque of the input shaft 57 to the largediameter gear 53 by way of the outer cylinder 58, the second smalldiameter helical gear 59xe2x80x2, the second largediameter helical gear 56b, and the second smalldiameter gear 54b. Therefore, the outer cylinder 58 is so constructed as to be slidable according to a difference between two thrust forces of mutually opposite directions generated by the first and second smalldiameter helical gears 59 and 59xe2x80x2, respectively. Here, since the phase difference between the first and second smalldiameter helical gears 59 and 59xe2x80x2 can be eliminated by the vertical slidable motion of the outer cylinder 58, it is possible to transmit the rotational torque uniformly through the two transmission routes.
In the above-mentioned helicopter power transmitting apparatus, however, as far as the rotational torque to be transmitted is small, since the outer cylinder can be well slid up and down, the rotational torque can be distributed uniformly. However, once the rotational torque exceeds a predetermined value, since a frictional force between the outer cylinder 58 and the input shaft 57 increases, the outer cylinder 58 cannot slide. Therefore, when the load of the helicopter is large, there exists a problem in that the rotational torques transmitted from the first and second smalldiameter gears 54a and 54b to the largediameter gear 53, respectively are not well balanced.
To overcome the above-mentioned problem, although the non-slidable condition due to increased friction of the outer cylinder may be somewhat improved by using a ball-splined joint structure such that balls intervene between the input shaft and the outer cylinder, there arises another problem in that the apparatus is rather complicated and thereby becomes costly.
Therefore, the object of the present invention is to provide the helicopter power transmitting apparatus which can transmit the engine input to the main rotor, etc. through the pair of the gear trains securely and smoothly, in spite of a simple construction.
With these problems in mind, therefore, it is the object of the present invention to provide a helicopter power transmitting apparatus of a simple construction, which can securely and uniformly transmit an engine output power to a main rotor, etc. through a pair of gear trains.
To achieve the above-mentioned object, the first aspect of the present invention provides a helicopter power transmitting apparatus including: a largediameter gear (3) linked with a main rotor driving shaft (2); first and second smalldiameter gears (4a, 4b) both having the same diameter and the same number of teeth and arranged at a predetermined angular interval in mesh with said largediameter gear, respectively; a first largediameter helical gear (6a) linked with said first smalldiameter gear (4a) via a first shaft (5a) over said first smalldiameter gear (4a); a second largediameter helical gear (6b) linked with said second smalldiameter gear (4b) via a second shaft (5b) under said second smalldiameter gear (4b), both the first and second largediameter helical gears (6a, 6b) having the same diameter and the same number of teeth but opposite tooth inclination direction with respect to each other; an input shaft (7) arranged in parallel to the first and second shafts (5a, 5b), to transmit rotational torque generated by an engine; an outer cylinder (8) fitted to an outside of said input shaft (7), slidably in axial direction of said input shaft (7); and first and second smalldiameter helical gears (9, 9xe2x80x2) fixed to both upper and lower ends of said outer cylinder in mesh with said first and second largediameter helical gears (6a, 6b), respectively, wherein said first and second shafts (5a, 5b) have such flexural rigidity relationship as to substantially eliminate a phase difference between the first and second smalldiameter gears (4a, 4b), against unbalanced forces applied to said first and second shafts (5a, 5b), respectively when said first and second smalldiameter gears (4a, 4b) transmit the same torque to said largediameter gear (3).
Further, the first aspect of the present invention provides a helicopter power transmitting apparatus including: a largediameter gear (3) linked with a main rotor driving shaft (2); first and second smalldiameter gears (4a, 4b) both having the same diameter and the same number of teeth and arranged at a predetermined angular interval and brought into mesh with said largediameter gear (3) in sequence along rotational direction of said largediameter gear (3), respectively; a first largediameter helical gear (6a) linked with said first smalldiameter gear (4a) via a first shaft (5a) over or under said first smalldiameter gear (4a); a second largediameter helical gear (6b) linked with said second smalldiameter gear (4b) via a second shaft (5b) over or under said second smalldiameter gear (4b) on opposite side to said first largediameter gear (6a), both the first and second largediameter helical gears (6a, 6b) having the same diameter and the same number of teeth but opposite tooth inclination direction with respect to each other; an input shaft (7) arranged in parallel to the first and second shafts (5a, 5b) to transmit rotational torque generated by an engine; an outer cylinder (8) fitted to an outside of said input shaft (7) and arranged in axial direction of said input shaft; and first and second smalldiameter helical gears (9, 9xe2x80x2) fixed to both upper and lower ends of said outer cylinder in mesh with said first and second largediameter helical gears (6a, 6b), respectively,
wherein said first shafts (5a) has a flexural rigidity higher than that of said second shaft (5b).
Here, it is preferable that said input shaft (7) is provided with splines on an outer circumferential surface thereof, and said outer cylinder (8) is axially and slidably fitted to the splines of said input shaft.
Further, the second aspect of the present invention provides a helicopter power transmitting apparatus including: a largediameter gear (3) linked with a main rotor driving shaft (2); first and second smalldiameter gears (4a, 4b) both having the same diameter and the same number of teeth and arranged at a predetermined angular interval and brought into mesh with said largediameter gear in sequence along rotational direction of said large-diameter gear, respectively; a first largediameter helical gear (6a) linked with said first smalldiameter gear (4a) via a first shaft (5a) over or under said first smalldiameter gear (4a); a second largediameter helical gear (6b) linked with said second smalldiameter gear (4b) via a second shaft (5b) over or under said second smalldiameter gear (4b) on opposite side to said first largediameter gear (6a), both the first and second largediameter helical gears (6a, 6b) having the same diameter and the same number of teeth but opposite tooth inclination direction with respect to each other; a third shaft (21) arranged between and roughly in parallel to the first and second shafts (5a, 5b), slidably in axial direction thereof; first and second smalldiameter helical gears (9, 9xe2x80x2) fixed to upper and lower ends of said third shaft (21) in mesh with said first and second largediameter helical gears (6a, 6b), respectively; and an input shaft (7) linked with an end of said third shaft (21) in the vicinity of said first largediameter helical gear (6a) to transmit rotational torque generated by an engine, via a slidable joint (22) for allowing axial movement of said third shaft (21) and for transmitting torque.
Here, it is preferable that said third shaft (21) has such a torsional rigidity as to substantially eliminate a phase difference between the first and second smalldiameter gears (4a, 4b), against unbalanced forces applied to said first and second shafts (5a, 5b), respectively when said first and second smalldiameter gears (4a, 4b) transmit the same torque to said largediameter gear (3).
Further, it is preferable that the slidable joint (22) includes an end of said third shaft (21) formed with splines on an outer circumferential surface thereof, and an end of said input shaft (7) formed with a shape fitted to the splines of the end of said third shaft (21) to allow axial movement of said third shaft.
Further, the third aspect of the present invention provides a helicopter power transmitting apparatus including: a largediameter gear (3) linked with a main rotor driving shaft (2); first and second smalldiameter gears (4a, 4b) both having the same diameter and the same number of teeth and arranged at a predetermined angular interval and brought into mesh with said largediameter gear in sequence along rotational direction of said largediameter gear; a first largediameter helical gear (6a) linked with said first smalldiameter gear (4a) via a first shaft (5a) over or under said first smalldiameter gear (4a); a second largediameter helical gear (6b) linked with said second smalldiameter gear (4b) via a second shaft (5b) longer than said first shaft (5a) over or under said second smalldiameter gear (4b) on the same side as said first largediameter gear (6a), both the first and second largediameter helical gears (6a, 6b) having the same diameter and the same number of teeth but opposite tooth inclination direction with respect to each other; a third shaft (31) arranged in parallel to said first and second shafts (5a, 5b) in axial direction thereof; first and second smalldiameter helical gears (9, 9xe2x80x2) fixed to upper and lower ends of said third shaft (31) in mesh with said first and second largediameter helical gears (6a, 6b), respectively; and an input shaft (7) linked with an end of said third shaft (31) in the vicinity of said first largediameter helical gear (6a) to transmit rotational torque generated by an engine via a slidable joint (32) for allowing axial movement of said third shaft (31) and for transmitting torque.
Here, it is preferable that said first and second shafts (5a, 5b) have such flexural rigidity relationship as to substantially eliminate a phase difference between the first and second smalldiameter gears (4a, 4b), against unbalanced forces applied to said first and second shafts (5a, 5b), respectively when said first and second smalldiameter gears (4a, 4b) transmit the same torque to said largediameter gear (3); and further said third shaft (31) has such a torsional rigidity as to substantially eliminate the phase difference between the first and second smalldiameter gears (4a, 4b) when said first and second smalldiameter gears (4a, 4b) transmit the same torque to said largediameter gear (3).
Further, it is preferable that the slidable joint (32) includes an end of said third shaft (31) formed with splines on an outer circumferential surface thereof, and the end of said input shaft (7) formed with a shape fitted to the splines of the end of said third shaft (31) to allow axial movement of said third shaft.
In the helicopter power transmitting apparatus according to the present invention, since the flexural rigidity and the torsional rigidity of the first shaft (5a), the second shaft (5b) and the third shaft (31) are respectively adjusted appropriately, it is possible to uniformly distribute the rotational torques transmitted by the first and second smalldiameter gears (4a) and (4b) to the large-diameter gear (3), respectively without changing or without complicating the composing elements of the helicopter power transmitting apparatus.